# I Know You Don’t Care, But…

The BBC reports that the E8 Lie Group has been mapped. Professor David Vogan from the Massachusetts Institute of Technology (MIT) announced the feat in a lecture titled: *The Character Table for E8, or How We Wrote Down a 453,060 x 453,060 Matrix and Found Happiness*.

Almost no one is interested that 19 mathematician spent fours years doing this and it took three days to calculate the final computation on a supercomputer. Working in 248 dimensions isn’t even conceivable for most of the world, but it is a very good thing and will help us understand basic scientific interactions. It will also allow us to do things with a computer simulation that would have required spending hundred of millions or billions of dollars if we tried to construct the equipment needed for experiments.

Think about all of the time and effort expended in producing 3D images, now add the other 245 dimensions.

12 comments

The Culture Ghost{ 03.19.07 at 1:06 pm }Far out.

What’s it mean?

Bryan{ 03.19.07 at 2:41 pm }It means we can really start to understand string theory, and start to build models of the universe that include all of the factors involved. We can start to understand the shift from Isaac Newton to Albert Einstein to Stephen Hawking. We can begin to understand dark matter and world holes. This is really base level research. We can test things against the E8 model as a reality check. It is a new measurement tool.

jamsodonnell{ 03.19.07 at 3:10 pm }I never really was much cop at maths or physics. I rmember watching a programme on BBC here a few years back (Horizon, a long running science series) the prog was about a row over whetner there were 10 or 11 dimensions (or was it 11 or 12?) Sadly my eyes just glazed over as did the not-wife’s! Give me mammalian physiology and I knowe where I am (or where I was – it’s 23 years since I graduateed)

Bryan{ 03.19.07 at 4:32 pm }This is a very limited field of specialists, and not many people could understand what they were talking about because it involves a vocabulary that is mostly symbols, but most computer users would have some idea what a spreadsheet is, and this is a spreadsheet with a half million columns and a half million rows.

The Culture Ghost{ 03.19.07 at 4:41 pm }If it advances the “understanding” of string theory…deal me in.

Bryan{ 03.19.07 at 5:03 pm }The string guys are all saying “aha!” so I think it is good news for them.

The Culture Ghost{ 03.19.07 at 6:04 pm }String theory has been on the ropes (so to speak) in some recently published books. The anit-string crowd has been going after it as being “unprovable” and ultimately a dead end towards a Grand Unified Theory. In some of the stuff I’ve read I’ve been tracking up to and through seven dimensions, but when they get into the tenth and eleventh dimensions: brain go “pop.”

If the string guys are happy, maybe I’ll be less confused sometime in the future.

Bryan{ 03.19.07 at 7:16 pm }As I understand it, this is another measurement tool/template for understanding relationships. The thing is, if the theoretical math guys can express the relationships, then they can be programmed. If the computer can be used then the process speeds up. You can’t program what you don’t know. First you have to do it by hand so you know how to tell the computer what needs to be done. Then you can use the computer to check what you’ve done and if you both agree, it’s real.

You can’t map lands you’ve never seen.

Steve Bates{ 03.19.07 at 8:04 pm }It must have been something E8…

My understanding from Lisa Randall’s book is that there is something of a truce at the moment regarding string theory. The objection from its critics is not that it cannot be proved, but that it cannot be observed experimentally at any energies that can be… or are ever likely to be… created in any collider or similar apparatus. String theorists construct abstract models, then look for resemblance to well-established aspects of known reality. Sometimes they find them. But they cannot do experiments with the strings themselves. Anything that gives string theorists more powerful analytical tools is very much to their benefit, as they have no experimental tools.

Bryan{ 03.19.07 at 8:59 pm }This should eventually provide the basis for building the necessary models to test theories in many different fields. You have to have the math before you can have the models.

Jim{ 03.19.07 at 9:22 pm }I’ll take a crack at why this is important, but it is far enough outside of my expertise that my description should come with a grain of salt.

I learned a little group theory as a grad student in solid-state physics (20 years ago). For a massive HW assignment I had to take a messy 40 x 40 matrix and tame it with the tools of group theory. The Prof. said, “I’m giving you three weeks to do it because you really need four!” — he wasn’t kidding. So, I’ll pass on the 453,060 x 453,060 matrix!

The significance of group theory is that it is a mathematical framework that allows one to understand the role of symmetry in geometries and systems of equations.[*]

For a physicist, symmetries are particularly useful because of Noether’s theorem, which states that for any symmetry of a physical system there must be some quantity that is conserved.

For example, if the laws of physics are the same at all times (i.e., if running a given experiment identically at two different times must give the same result) it turns out that the conserved quantity is the total energy of the system (aka the First Law of Thermodynamics).

Similarly, if the laws of physics are the same everywhere in the universe you get the conservation of linear momentum (also called just “momentum”). And, if the laws of physics are the same regardless of the orientation of the experiment (i.e., there is no preferred direction in space) then you get the conservation of angular momentum.

The tie to string theory? My understanding is that you decide what quantities have to be conserved if string theory is to work, then determine the symmetries that give rise to conserved quantities. Evidently the group that contains all required symmetries for superstrings is E8. If all of the details of E8 were worked out, then one would have an arsenal of mathematical relationships to employ in trying to understand the ramifications of string theory.

And that is why this is a big deal.

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[*] How do geometries and systems of equations relate, you ask? Equations can be considered as describing a geometrical object. E.g., y = 3x + 4 describes a particular line in a plane. If you want to generically describe all lines you write y = ax + b, where a and b are constants whose values determine which particular line is under consideration.

(If you recall your H.S. algebra and geometry, you might remember that a = the slope of the line and b = the point where the line crosses the y-axis.)

Any statements you can make that are true for all values of a and b are therefore statements that are true about all lines. Conversely, any statement you can make that are true about all lines are statements that are true about all equations of the form y = ax +b.

For example, I might need to solve two simultaneous equations:

[Eq. 1] y = ax + b

[Eq. 2] y = cx + d

For a given set of constants a, b, c, and d, there might be one point {x,y} which satisfies both equations. That particular pair of values {x, y} is the solution to the simultaneous equations.

It is possible that there is no solution for a particular set of constants a, b, c, and d. Is there an easy way to find out if a solution exists?

Remember that these equations describe straight lines. Two lines on a plane have to cross at some point {x, y} — unless they are parallel. (If they cross, the coordinates {x, y} of the crossing point is the solution to the simultaneous equations.)

If two lines are parallel, how do their equations relate? Well, parallel lines must have the same slope, so the value of “a” in Eq. 1 must be the same as the value of “c” in Eq. 2.

So, if I have two equations like Eq. 1 & 2, but a = c, then there is no {x, y} pair that satisfies both equations.

Group theory allows the argument above to be formulated as a set of mathematical relationships, rather than as an exercise in logic.

Bryan{ 03.19.07 at 10:14 pm }This is why I love the Internet – seek and ye shall find, or just wait around and the answer will come.

We should be able to really make some progress with string theory, one way or another.

I’m burdened by the fact that I can visualize it, but I can’t explain what I visualize because I understand math at an intuitive level – I know the answer, but I can’t explain how I got it, which is actually pretty worthless in upper level math.